A brittle material substrate is generally cut using a method to be described below. First, a scribe line including a vertically-formed crack (hereinafter, referred to as “vertical crack”) is formed along a desired line to be cut on one surface of a brittle material substrate using such as sintered diamond cutter wheel, laser irradiation apparatus or the like (hereinafter, referred to as “scribing step”). Thereafter, a pressure is applied upon the brittle material substrate along the scribe line, or the brittle material substrate is bent along the scribe line, thereby affecting a pulling force on substrate portions located on both sides of the scribe line to extend the vertical crack in a thickness direction of the brittle material substrate so as to reach the other surface (hereinafter, referred to as “bottom surface”) of the substrate G. As such, the brittle material substrate is cut along the scribe line (hereinafter, referred to as “breaking step”).
Reference 1 discloses a conventional cutting apparatus for performing the breaking step described above. The conventional cutting apparatus for performing the breaking step described above will be described with reference to FIG. 14 and FIG. 15. A cutting apparatus 6 shown in FIG. 14 includes: a table 630 (see FIG. 15) for holding a substrate G formed with a scribe line thereon; a first auxiliary roller 611 and a second auxiliary roller 621 arranged with the table 630 therebetween so as to oppose each other in an upper and lower direction; a substrate holding break roller 612 and a pressing break roller 622 arranged with the substrate G therebetween so as to oppose each other in the upper and lower direction; and a third auxiliary roller 613 and a fourth auxiliary roller 623 arranged with the substrate G therebetween so as to oppose each other in the upper and lower direction.
The first auxiliary roller 611 and the second auxiliary roller 621, the substrate holding break roller 612 and the pressing break roller 622, and the third auxiliary roller 613 and the fourth roller 623 are arranged such that central portions thereof in their axial direction are approximately aligned, respectively.
When the breaking step is performed by the cutting apparatus 6, the substrate G is mounted on the table 630 such that the central portion of each of the rollers 611 to 613 and 621 to 623 in its axial direction is approximately aligned with a scribe line S formed on the substrate G, as shown in FIG. 15. Next, the first auxiliary roller 611 and the second auxiliary roller 621, and the third auxiliary roller 613 and the fourth auxiliary roller 623 are each moved to a position by an air cylinder so as to contact the substrate G and held there. In addition, the substrate holding break roller 612 and the pressing break roller 622 are each moved to a position where they are each pressed upon the substrate G by a motor M with a predetermined pressure and held there. The rollers 611 to 613 and 621 to 623 are entirely moved in +X direction such that the rollers 611 to 613 and 621 to 623 are moved along the scribe line S. As such, the first auxiliary roller 611 and the second auxiliary roller 621, the substrate holding break roller 612 and the pressing break roller 622, and the third auxiliary roller 613 and the fourth auxiliary roller 623 are sequentially rolled on a top surface and a bottom surface of the substrate G along the scribe line S, respectively.
An operation for cutting the brittle substrate material by performing the breaking step by the cutting apparatus 6 will be described in detail with reference to FIG. 15. FIG. 15 is a schematic view for describing an operation of each of the rollers 611 to 613 and 621 to 623 included in the cutting apparatus 6.
The pressing break roller 622 arranged below the substrate G presses a portion on the bottom surface of the substrate G upward that corresponds to the scribe line S. The substrate holding break roller 612 arranged so as to oppose the pressing break roller 622 presses portions on both sides of the scribe line S on the top surface of the substrate G downward. In this case, the portions on both sides of the scribe line S pressed by the substrate holding break roller 612 correspond to portions on both sides of the portion that corresponds to the scribe line S on the substrate G and that is pressed upward by the pressing break roller 622. The portion of the substrate G formed with the scribe line S is pressed upward by the pressing break roller 622, and at the same the time, the portions on both sides of the portion are pressed downward by the substrate holding break roller 612. In such a state, the substrate holding break roller 612 and the pressing break roller 622 are rolled on the top surface and the bottom surface of the substrate G along the scribe line S, respectively.
As such, a vertical crack forming the scribe line S is sequentially expanded from the top surface of the substrate G, and the vertical crack is extended in a thickness direction of the substrate G to reach the bottom surface of the substrate G. As a result, the substrate G is cut.
The first auxiliary roller 611 and the second auxiliary roller 621, and the third auxiliary roller 613 and the fourth auxiliary roller 614 are each a columnar roller having an outer circumferential surface thereof with a predetermined diameter. The first auxiliary roller 611 and the second auxiliary roller 621 suppress a distortion of the substrate G before the cutting of the substrate G and prevent the vertical crack from extending in any directions other than a vertical direction. The third auxiliary roller 613 and the fourth auxiliary roller 623 suppress a distortion of the substrate G after the cutting of the substrate G and prevent cut faces B1 and B2 of newly-formed substrate portions by cutting the substrate G from contacting each other in an inclined state.    Reference 1: International Publication WO 2004/096721 pamphlet